Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
FLORISTICS, STAND STRUCTURE AND ABOVEGROUND
BIOMASS OF A 25-HA RAINFOREST PLOT IN THE WET
TROPICS OF AUSTRALIA
MG Bradford1, DJ Metcalfe2, A Ford1, MJ Liddell3 & A McKeown4
1
CSIRO Land and Water, Tropical Forest Research Centre, PO Box 780, Atherton, 4883 Australia; Matt.Bradford@
csiro.au
2
CSIRO Land and Water, Ecosciences Precinct, Brisbane, 4102 Australia
3
School of Pharmacy and Molecular Sciences, James Cook University, Cairns, 4878 Australia
4
CSIRO Land and Water, James Cook University Campus, Cairns, 4878 Australia
Received August 2013
BRADFORD MG, METCALFE DJ, FORD A, LIDDELL MJ & MCKEOWN A. 2014. Floristics, stand
structure and aboveground biomass of a 25-ha rainforest plot in the wet tropics of Australia. Australian
wet tropical rainforests are both floristically diverse and high in endemism, and their restricted distribution
sees them particularly vulnerable to climate change and other anthropogenic influences. Historically, there
were no large-scale studies of the dynamics and drivers of these systems in Australia. We established a 25ha rainforest plot in the Wet Tropics bioregion of Australia to undertake intensive collection of floristic,
structural and ecosystem measurements. An initial census of all stems ≥ 10 cm diameter at breast height (dbh)
recorded 23,416 stems from 208 species in 128 genera and 53 families; Lauraceae, Rutaceae, Proteaceae and
Elaeocarpaceae were dominant. Endemism was high with 80.3% of species of stems ≥ 10 cm dbh found on the
plot endemic to Australia and 45.2% endemic to the Wet Tropics bioregion. We provide the first measured
estimate of basal area (52.0 m2 ha-1) and aboveground living biomass (418.5 Mg ha-1) for a large area of
Australian rainforest. The data collected from the 25-ha plot provide a baseline description of floristics and
stand structure that will facilitate and encourage long-term ecological research of forest dynamics and allow
direct comparisons to be made with similar plots on a global scale.
Keywords: Stem density, basal area, climate change, Queensland, Robson Creek
INTRODUCTION
Tropical rainforests are recognised as valuable
for their intrinsic worth, the biodiversity they
support, the ecosystem services they provide,
their utilitarian worth for timber and nontimber products and the potential that they
have for ameliorating the impacts of climate
change on the local to global scale. However,
we still have limited understanding of their
dynamics and capacity to adapt to change,
an understanding which requires largescale, long-term monitoring approaches. An
effective option for large-scale, long-term
monitoring of forests is the establishment
of large focused plots (Condit 1995, 1998,
Lindenmayer et al. 2012) and associated
observation infrastructure.
In Australia, a small number of largescale, long-term ecosystem monitoring sites
© Forest Research Institute Malaysia
543
are maintained (Lindenmayer et al. 2014),
few of which are located in the tropics and
these focusing on savannah communities
(e.g. Kutt & Woinarski 2007, Russell-Smith
et al. 2010). Although rainforest in Australia
only occupies 0.5% of the land mass, it is
recognised as an internationally important
biome due to high levels of plant and animal
diversity and endemism, its disproportionate
influence on the water balance and climate,
and its suitability for in-situ conser vation of
threatened species of outstanding universal
value (Wet Tropics Management Authority
2013). For these reasons, the wet tropical
rainforest of Queensland was chosen to locate
a large-scale monitoring plot comparable with
other long-term forest plots around the globe
(Condit 1998). Previous to the establishment
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
of this plot, long-term monitoring of tropical
rainforest was achieved via a series of smaller
permanent plots (Metcalfe & Bradford 2008,
Theimer et al. 2011, Murphy et al. 2013).
The Wet Tropics bioregion of Australia is
situated along the tropical east coast of Australia
stretching some 450 km from 15° 40' S to 19°
15' S and covering approximately 2 million
ha (Sattler & Williams 1999). The bioregion
consists of narrow coastal floodplains flanked
by steep mountains to 1600 m above sea level
(asl) and contains a mosaic of vegetation types,
many associated with particular landforms.
North of the bioregion, the forests of Cape York
are dominated by sclerophyll vegetation types,
with small areas of mostly monsoonal rainforest
with a pronounced dr y season. South and
west of the bioregion the forests become more
sclerophyll-dominated in character, and give way
to woodlands and savannah as the influence of
coastal rainfall diminishes and fire becomes a
more important driver of vegetation patterns
(Bowman 2000, Metcalfe & Ford 2008).
The Robson Creek 25-ha rainforest plot was
established as the centrepiece of the Robson
Creek node of the Far North Queensland
Rainforest Supersite (TERN 2013). The plot
lies in the centre of the Wet Tropics bioregion
and was chosen as a representative mid-altitude
(700 m asl) site. The census plot is of national
value in that it provides the first large-scale
investigation of rainforest diversity and forest
dynamics in Australia. It is also of global value
as it allows direct comparisons with similarly
structured plots around the world as part
of the Smithsonian Institution’s Centre for
Tropical Forest Science plot network (Condit
1998). The features of Australian wet tropical
rainforests are frequent disturbance by tropical
cyclones (hurricanes/typhoons), high levels of
floristic and faunal endemism, and floristic and
faunal affinities with both Indo-Malayan and
Gondwanan taxa (Metcalfe & Ford 2008).
In this paper we provide an analysis of the
stems ≥ 10 cm diameter at breast height (dbh)
on the Robson Creek 25-ha plot and of the
vascular plants of a core hectare within the
25 ha. Data are from the first census, completed
in December 2012. The data form a baseline
description of diversity and stand structure that
will facilitate and encourage long-term ecological
research on the plot and allow direct comparisons
to be made with similar plots on a global scale.
© Forest Research Institute Malaysia
544
MATERIALS AND METHODS
Study area
The Robson Creek 25-ha rainforest plot is
located approximately 30 km north-east of
Atherton, in North Queensland, Australia,
17° 07' S, 145° 37' E, at 680–740 m elevation.
It lies in Danbulla National Park within the
Wet Tropics World Heritage Area. The plot is
moderately inclined with a low relief (Speight
2009) although the Lamb Range rises sharply to
1276 m asl immediately to the north of the plot.
Three permanent creeks flow through the plot,
joining with Robson Creek which in turn meets
the man-made Tinaroo Dam on the Barron River
approximately two kilometres south of the plot.
LiDAR and hyperspectoral data collection flights
were flown in 2012 by the AusCover facility of
the Australian Terrestrial Ecosystem Research
Network (TERN 2013). Figure 1 shows the
resultant contour map of the 25-ha area.
The vegetation on the plot is described as
complex mesophyll vine forest on granite and
meta-sediment alluvium (Regional Ecosystem
(RE) 7.3.36a, Queensland Government 2006),
although higher sections of the plot are analogous
to simple notophyll vine forest on meta-sediment
(RE 7.11.12a). The forest type changes to simple
to complex notophyll vine forest on granite (RE
7.12.16a) with increasing altitude to the north
of the plot. The parent material on the plot is
meta-sedimentary and soil fertility is moderately
low. Using the Australian Soil Classification
system, the soil has been classified as an acidic,
dystrophic, brown dermosol; medium, nongravelly, clayey/clayey, moderate (Nelson &
Liddell 2013, unpublished data).
The climate of the area is considered seasonal
with 61% of annual rainfall occurring between
January and March (Figure 2; Australian Bureau
of Meteorology 2012). Mean annual rainfall at
Danbulla Forestry Station (4.5 km south of the
plot) is 1597 mm (1921–1991). Mean monthly
minimum and maximum temperatures for Kairi
Research Station, where the nearest data are
collected, are shown in Figure 2 (Australian
Bureau of Meteorology 2012). An automatic
weather station (Environdata Weathermaster
2000) was set up in 2011 at Robson Creek and the
first two complete years of data show comparable
intra-annual patterns as those obser ved at
Danbulla Forestry Station and Kairi Research
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Figure 1
Bradford MG et al.
The Robson Creek 25-ha rainforest plot showing 2-m contours, permanent watercourses (solid
black lines) and the access track (broken black line) which follows an abandoned logging track;
the 100 m × 100 m grid shows each of the 25 ha; the single core hectare (ha 6) is located on the
western edge of the plot
Station in both rainfall and temperature. The site
may be regarded as moist rather than wet and has
an annual mean relative humidity of 82%.
The Robson Creek 25-ha rainforest plot and
the Daintree Rainforest Observatory (Laidlaw et
al. 2007) comprise the two operational nodes of
the Far North Queensland Rainforest Supersite.
The Daintree Rainforest Observatory currently
comprises two single-hectare lowland rainforest
plots with a canopy crane and is situated on the
coast 115 km to the north of the Robson Creek
plot. The Far North Queensland Rainforest
Supersite is one of 10 supersites located across
Australia to represent important ecological
© Forest Research Institute Malaysia
biomes. Supersites were established as part of the
Terrestrial Ecosystem Research Network (TERN)
(TERN 2013) through a major infrastructure
investment. Data from the supersites can be
accessed via the Australian Supersite Network
data portal (http://www.tern-supersites.net.
au/knb). The plot is also part of the Centre for
Tropical Forest Science (CTFS) global network
of forest research plots (http://www.ctfs.si.edu).
Disturbance
While the region has been occupied by aboriginal
people for at least 8000 years (Hill et al. 2011),
545
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
Figure 2 Mean monthly rainfalls (Y left axis, solid line, Danbulla Forestry 1921–1991) and mean monthly
maximum and minimum temperatures (Y right axis, broken lines, Kairi Research Station 1913–
2011); note the highly seasonal summer-wet, winter-dry patterns of rainfall in the region
traditional use of the Robson Creek area by the
Tablelands Yadinji had ceased by the 1960s. Due
to the low population density, it is unlikely that
the original inhabitants contributed significantly
to rainforest dynamics except in small areas, with
only very selective timber harvesting, clearing
and burning taking place. As is the case for all
accessible areas of the Wet Tropics of Australia,
the Robson Creek 25-ha plot was selectively
logged with the last logging undertaken between
1960 and 1969. The southern and central parts
of the plot were logged between 1960 and 1964
while the north-east and north-west corners
were logged between 1964 and 1969. Logging
frequency and intensity are not available as
logging records were not retained; however,
logging practices can be inferred from Crome et
al. (1992). Of particular interest is that logging
was not practised within 10 m either side of
watercourses and a species preference list was
adhered to. Seven very highly desired and six
highly desired species on the preference list
are currently present on the plot. Silvicultural
treatment of forest in the Wet Tropics was
common in the 1950s. Treatments included
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546
removal of species not on the preference list,
promotion of desired timber species, and
retention of larger individuals as seed trees.
Although no evidence exists of such treatments
on the plot, the presence of such an activity
cannot be dismissed.
Plot establishment and census
Each hectare corner of the Robson Creek
25-ha rainforest plot was surveyed to a horizontal
plan projection aligned to grid north using a
differential Global Positioning System (Trimble
Pro XRT using the Omnistar DGPS signal)
resulting in an independent precision of each
survey point of 2.3 m ± 1.8 SD.
All stems on the 25-ha plot (trees, lianas,
ferns, palms, strangler figs) with dbh ≥10 cm were
identified to species, mapped, tagged, heighted
and the dbh measured. Nomenclature followed
Bostock and Holland (2010). Stems were mapped
within a 20 m × 20 m subplot to an accuracy of
± 0.5 m. Stems were permanently marked with
a tag attached to stainless steel wire encircling
the stem for stems < 30 cm dbh or a painted
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
number for all larger stems. Height (length
of stem) was measured to ± 0.5 m with a laser
rangefinder or estimated against a previously
measured tree. The dbh was measured according
to protocols outlined in Condit (1998) with
one variation: for species known to exhibit
buttressing on larger specimens, the point
of measurement was pre-emptively elevated
above the predicted buttressing influence.
The point of measurement was decided by
the team leader and was species specific. This
may result in minor underestimations of basal
area and aboveground biomass. In addition to
the ≥ 10 cm dbh stem census, (1) a complete
vascular plant inventory was carried out on a
single core hectare (ha 6) and (2) basal area
and biomass estimations of stems ≥ 1 cm and
< 10 cm dbh were determined from dbh and
height measurements of these stems in 2 ha.
Fieldwork was carried out between December
2009 and November 2012. Voucher specimens
are held in the Queensland Herbarium (BRI)
and Australian Tropical Herbarium (CNS) with
duplicate specimens distributed elsewhere.
Data analysis
Aboveground biomass (AGB) of stems > 10 cm
dbh was calculated using the Chave et al. (2005)
algorithm for moist forests:
AGB = 0.0509 × wood density × dbh2 × height
Wood density values were taken from a
database of species from northern Australia
(CSIRO unpublished). For stems ≥ 1 cm to
< 10 cm dbh the same Chave et al. (2005)
algorithm was used and a single wood density
value of 0.50 g cm-3 was assigned to each stem
(the mean wood density value of the plot was
0.56 g cm-3). Diversity measures were calculated
using PRIMER 6 following Clarke and Gorley
(2006). Relative frequency, relative density,
relative dominance and the importance value
index for species were calculated for all stems
≥ 10 cm dbh following Curtis (1959). Relative
frequency was calculated by hectare. We used
the family importance value (Mori et al. 1983) to
calculate dominant families as this value stresses
species diversity within a family.
RESULTS
Floristics
The 25-ha plot census recorded 23,416 stems
≥ 10 cm dbh consisting of 208 species from
128 genera and 53 families. The most common
species were the canopy trees Litsea leefeana
(Lauraceae) with 7.9% of stems, Cardwellia sublimis
(Proteaceae) 6.6% and Flindersia bourjotiana
(Rutaceae) 5.6%. Twenty-five species were
represented by a single stem ≥ 10 cm dbh. The
most common families were Lauraceae (19.9%
of stems), Rutaceae (17.2%) and Proteaceae
(14.2%). The number of species per hectare
ranged from 82 to 118 (mean 98.2 ± 9.9 SD).
Diversity measures for the 25-ha plot are shown
in Table 1. The dominant species and families
are shown in Tables 2 and 3. Trees contributed
192 species while lianas contributed nine species
(27 stems), strangler figs four species (23 stems),
epiphytes two species (7 stems), and ferns one
species (14 stems). Palms ≥ 10 cm dbh were
absent from the plot.
The core 1-ha vascular plant survey revealed
266 species from 189 genera and 82 families. The
most common families were Lauraceae (8.8%
of species), Sapindaceae (6.6%) and Myrtaceae
(6.2%). No exotic species were recorded as stems
≥ 10 cm dbh or on the core hectare; however, two
stems of the naturalised Solanum mauritianum
(Solanaceae), a transient pioneer tree, were
found within the 25-ha plot.
Table 1 Stem diversity measures for stems ≥ 10 cm dbh on the
Robson Creek 25-ha rainforest plot
N
S
d
J'
H'
1–ʎ
23,416
208
20.57
0.778
4.15
0.973
N = number of stems, S = total number of species, d = Margalef’s species
richness index (S – 1)/log N, J' = Pielou’s evenness index H'/log S, H' =
Shannon diversity index ∑(Pi log Pi), 1 – ʎ = Simpsons evenness index 1 –
∑(Ni/N)2
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Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
Table 2 The 10 most important species from stems ≥ 10 cm dbh on the Robson Creek 25-ha rainforest plot
calculated using the importance value index (Curtis 1959)
Species
Cardwellia sublimis
Litsea leefeana
Flindersia bourjotiana
Flindersia pimenteliana
Elaeocarpus largiflorens subsp. largiflorens
Flindersia brayleyana
Doryphora aromatica
Alphitonia whitei
Darlingia darlingiana
Sloanea australis subsp. parviflora
D
F
BA
RDe
RF
RDo
1540
1837
1322
774
953
496
596
851
687
507
25
25
25
24
25
25
25
25
25
23
88.32
61.85
72.28
60.72
36.10
47.81
42.32
25.58
26.50
30.11
6.58
7.85
5.65
3.31
4.07
2.12
2.55
3.63
2.93
2.17
1.02
1.02
1.02
0.98
1.02
1.02
1.02
1.02
1.02
0.94
7.87
5.51
6.44
5.41
3.22
4.26
3.77
2.28
2.36
2.68
Importance
value index
15.46
14.37
13.10
9.69
8.30
7.40
7.33
6.92
6.31
5.78
D = stem density, F = number of hectares present, BA = basal area (m2), RDe = relative density, RF = relative frequency,
RDo = relative dominance
Table 3
The 10 most important families from stems ≥ 10 cm dbh on the Robson Creek 25-ha
rainforest plot calculated using the family importance value (Mori et al. 1983)
Family
Lauraceae
Rutaceae
Proteaceae
Elaeocarpaceae
Sapindaceae
Cunoniaceae
Myrtaceae
Atherospermataceae
Rhamnaceae
Apocynaceae
N
Ni
BA
RDi
4668
4019
3343
2491
727
923
331
1312
909
486
30
14
14
11
19
7
19
2
3
6
181.0
246.8
174.3
126.0
12.7
65.9
26.5
54.6
30.3
22.2
0.14
0.07
0.07
0.06
0.09
0.03
0.09
0.01
0.01
0.03
RF
0.20
0.17
0.14
0.11
0.03
0.04
0.01
0.06
0.04
0.02
RDo
0.14
0.22
0.16
0.11
0.01
0.06
0.02
0.05
0.03
0.02
Family
importance
value
50.28
45.79
36.43
27.54
13.24
13.13
12.78
11.41
8.00
6.90
N = number of individuals, Ni = number of species, BA = basal area (m2), RDi = relative density, RF = relative
frequency, RDo = relative dominance
Endemism and biogeography
Stems ≥ 10 cm dbh revealed 20 genera considered
endemic to Australia and 11 genera endemic to
the Wet Tropics. Endemism is principally at the
species level; of the 208 species, 167 (80.3%) are
endemic to Australia and 94 (45.2%) are endemic
to the Wet Tropics bioregion. This is driven
largely by species within the families Lauraceae,
Myrtaceae, Proteaceae and Sapindaceae
(Table 4).
The core 1-ha vascular plant survey revealed
that 23 genera are endemic to Australia. Again,
endemism is principally at the species level; of the
266 species, 203 (76.3%) are considered endemic
© Forest Research Institute Malaysia
548
to Australia and 110 (41.3%) are endemic to
the Wet Tropics bioregion. Again, this is driven
largely by species within the families Lauraceae,
Myrtaceae, Proteaceae and Sapindaceae (Table 4).
No species have a distribution restricted to the
25-ha plot and close surrounds, although of the
Wet Tropic endemics present on the plot, 20
species (7.5%) are confined to the south of the
Black Mountain Corridor (Rossetto et al. 2007).
In this core 1 ha, 12.3% of the total Wet Tropics
rainforest flora is represented and near-basal
angiosperm lineages are well represented with 42
species or 24% of the total near-basal angiosperm
rainforest flora of the Wet Tropics (Metcalfe &
Ford 2009).
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
Table 4 The most speciose families from stems ≥ 10 cm dbh and the core 1 ha at the Robson Creek 25-ha
plot, and the number of species in those families endemic to Australia and the Wet Tropic bioregion
of Australia (WT)
Family
25-ha plot
Core 1 ha
Total species
Endemic to
Australia
Endemic to WT
Total species
Endemic to
Australia
Endemic to
WT
Lauraceae
30
27 (90)
14 (47)
23
21 (91)
11 (48)
Myrtaceae
19
18 (95)
11 (58)
17
17 (100)
12 (70)
Sapindaceae
19
14 (74)
6 (32)
18
14 (78)
7 (39)
Proteaceae
14
14 (100)
13 (93)
9
9 (100)
9 (100)
Rutaceae
14
10 (71)
6 (43)
13
9 (69)
5 (38)
Elaeocarpaceae
11
10 (91)
4 (36)
9
8 (89)
2 (22)
Numbers in parentheses refer to the percentages of total species
Stand structure
Canopy species attained a maximum height of
44 m on the plot although values of 25 to 30 m
were more common. The canopy was considered
uneven and no emergent stems were identified.
No species dominated the canopy although
L. leefeana, C. sublimis and F. bourjotiania were
most common. No species dominated the
subcanopy although Daphnandra repandula
(Atherspermataceae) and Toechima erythrocarpum
(Sapindaceae) were most common.
The largest diameter tree on the plot attained
152.5 cm dbh (Syzygium canicortex, Myrtaceae).
The frequency distribution of stem size classes
for stems ≥ 10 cm dbh is shown in Figure 3. The
stem density ≥ 10 cm dbh ranged from 714 to
1073 ha-1 (mean 936 ± 77 SD). The stem density
≥ 1 cm to < 10 cm dbh ranged from 9235 to
9417 ha-1 (mean 9326 ± 128 SD) in the 2 ha surveyed.
The survey of stems ≥ 1 cm and < 10 cm dbh
revealed that 13.7% (± 1.9 SD) of the basal area
was held in this size range. Incorporating this
value, the mean basal area of stems ≥ 1 cm dbh in
the 25 ha was 52.0 m2 ha-1 (± 4.5 SD) and ranged
from 45.5 to 62.6 m2 ha-1. For stems ≥ 10 cm dbh,
the species C. sublimis (7.9%), F. bourjotiana (6.5%)
and L. leefeana (5.5%) and the families Rutaceae
(22.0%), Lauraceae (16.1%) and Proteaceae
(15.5%) contributed the greatest basal area.
Aboveground biomass (AGB)
The survey of stems ≥ 1 cm and < 10 cm dbh
revealed that 3.7% (± 0.3 SD) of AGB was held
in this size range. Incorporating this value, the
© Forest Research Institute Malaysia
549
mean AGB of stems ≥ 1 cm dbh in the 25 ha
was 418.5 Mg ha-1 (± 59.7 SD) and ranged from
306.3 to 561.5 Mg ha-1. For stems ≥ 10 cm dbh,
the species F. bourjotiana (6.7%), C. sublimis
(6.5%) and Flindersia pimenteliana (6.0%) and the
families Rutaceae (23.4%), Lauraceae (18.9%)
and Proteaceae (14.9%) provided the greatest
biomass. Figure 4 shows the distribution of basal
area and AGB across the stem sizes.
DISCUSSION
The floristic and structural analysis of the Robson
Creek 25-ha rainforest plot presented in this
study reflects the unique traits of Australian
Wet Tropical rainforests with high species
endemism, affiliations with both Indo-Malayan
and Gondwanan flora, and prevalence of tree
species of the families Lauraceae, Myrtaceae,
Sapindaceae and Proteaceae. In a summary of
the Wet Tropic rainforest of Australia, Metcalfe
and Ford (2008) report species endemism of
31.4% to the bioregion and 61.2% to Australia.
Our plot values of 44.9% (bioregion) and
80.3% (Australia) for stems ≥ 10 cm dbh and
41.3% and 76.3% for vascular species on the
core 1 ha are considerably higher, partly due
to the dominance of the near-basal Lauraceae
as well as the Myrtaceae and Proteaceae. High
levels of speciation in these and other families
are likely the result of historic persistence and
later isolation of the Wet Tropical rainforests in
Australia (Metcalfe & Ford 2008).
The rainforests of the Robson Creek 25-ha
rainforest plot and in the Wet Tropics generally
are structurally similar to the Indo-Malayan
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Number of stems
15,000
Bradford MG et al.
14,932
10,000
5000
0
Per cent of basal area and aboveground biomas
Figure 3 Frequency distribution of stems ≥ 10 cm dbh on the Robson Creek 25-ha rainforest plot; = numbers
above bars denote actual stem numbers for each dbh size class
Diameter (cm)
Figure 4 Frequency distribution of basal area (black fill) and aboveground biomass (grey fill) across stem
size classes on the Robson Creek 25-ha rainforest plot
forests, especially those of New Guinea, with
abundant climbing palms (Calamus spp.)
(Richards 1996). If New Guinea is included in
the Australian flora, species endemism rises to
91.8% for the trees ≥ 10 cm dbh and 85.3% for
vascular plants on the core 1 ha. There is some
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550
overlap of families, genera and, rarely, species
with forests in South-East Asia; the families
Myrtaceae, Lauraceae, Sapindaceae along with
Meliaceae are well represented in some SouthEast Asian forests (Sist & Saridan 1999, Lee
et al. 2002, Co et al. 2006). The most notable
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
absence from the Wet Tropics (and Australia)
is the family Dipterocarpaceae. There is also
considerable overlap with other regions which
may be loosely termed Gondwanan, suggesting
that ancestral taxa occurred on the super
continent before its breakup and separation
55 million years ago (Coleman 1980). Families
with Australian–Gondwanan origins presumably
include Cunoniaceae, Elaeocarpaceae, Ericaceae,
Monimiaceae (including Atherospermataceae),
Proteaceae, Podocarpaceae, Araucariaceae and
Winteraceae (Thorne 1986). These families, with
the exception of Ericaceae, are all represented
in the Robson Creek plot.
For the first time we report an estimate of
aboveground living biomass for an Australian
tropical rainforest derived from a comprehensive
ground sur vey of a large area. Previous
published values (Liddell et al. 2007, Preece et
al. 2012) have been based on small plot sizes
which may lead to unrepresentative estimates
particularly if large trees are present. Our value of
418.5 Mg ha-1 is generally comparable with those
for Indo-Malayan rainforests: 366–401 Mg ha-1
(Khairil et al. 2011), 271–478 Mg ha-1 (Laumonier
et al. 2010) and 403 Mg ha-1 (Hoshizaki et al.
2004); and higher than forests in the Amazon
basin: 125–387 Mg ha-1 (Baker et al. 2004).
Caution should be taken in assuming that
our biomass value is representative of old growth
forest in the Wet Tropics of Australia, as this tract
of forest and extensive areas of similar forests
in the region have been modified by logging
during the 20th century. Although logging was
seen as best practice at the time, it is considered
a major driver of stand structure change of both
this plot and Australian tropical rainforest in
general. Values for extracted timber in the Wet
Tropics (Crome et al. 1992) indicate that stem
(6.6 trees ha-1) and volume (37 m3 ha-1) losses
were minimal. However, the incidental damage
imposed on the forest, including 22% loss of
canopy cover, was presumably enough to alter
short-term growth and recruitment dynamics.
On the Robson creek plot the large proportion
of stems 10–20 cm dbh and the prominence
of successional species such as L. leefeana, C.
sublimis and F. bourjotiana more than 40 years
after logging ceased are evidence of this. Whether
the subsequent recruitment and growth of
such species have recovered or even exceeded
the biomass lost by extraction of timber and
associated incidental loss is debatable and cannot
© Forest Research Institute Malaysia
551
be tested as there are no comparable large areas
of unlogged forest. However, a 0.5-ha unlogged
plot adjacent to the Robson Creek plot has an
equivalent AGB of 700 Mg ha-1 (Murphy et al.
2013) which is considerably greater than values
recorded on the 25-ha plot.
Recent severe disturbance events in Australian
tropical rainforests are not restricted to
anthropogenic drivers. Cyclones are particularly
important structuring elements of rainforest
in the Wet Tropics of Australia with historical
data suggesting that a severe cyclone (categories
4–5) will cross a particular part of the coast of
Australia about once every 75 years (Turton &
Stork 2008). Severe cyclone Larry in 2006 caused
moderate structural damage to the forest on and
around the plot with a Bradford/Unwin damage
score (Metcalfe et al. 2008) of 3 on the plot
and the mortality of 74 trees ha-1 ≥10 cm dbh
(Metcalfe et al. 2008, Murphy et al. 2013) on
an adjacent CSIRO plot. Moreover, current
aggregations on the plot of large Blepharocarya
involucrigera (Anacardiaceae), a successional
species, suggest at least one large disturbance
event on a centurial time scale.
The Robson creek 25-ha rainforest plot was
established to undertake intensive collection
of ecosystem measurements to improve our
understanding of environmental change. For
the first time we present floristic and stand
structure information for a large forested area in
tropical Australia including taxa dominance, and
an estimate of rainforest basal area and aboveground biomass. The future addition of a census
of all stems to ≥ 1 cm dbh will give a complete
picture of woody plant diversity and bring the
Robson Creek plot into line with other large
plots around the world. In addition, baseline data
have been compiled for seedlings, vertebrates
and invertebrates on the plot, with ancillary
datasets monitoring soil and groundwater and
a canopy flux tower collecting atmospheric
flux data (http://www.tern-supersites.net.au/
knb). Together this information will allow us to
intensively monitor our ecosystem and detect
environmental change, including that caused
by human induced climate change. Australian
rainforests are considered floristically diverse,
are high in endemism, and their restricted
distribution sees them particularly vulnerable
to climate change and other anthropogenic
influences. The Robson creek 25-ha rainforest
plot is well placed to detect and monitor these
Journal of Tropical Forest Science 26(4): 543–553 (2014)
Bradford MG et al.
changes and contribute to our understanding of
global forest change.
ACKNOWLEDGEMENTS
This work was supported by the Australian
Supersite Network, part of the Australian
Government’s Terrestrial Ecosystems Research
Network (www.ter n.or g.au), a research
infrastructure facility established under the
National Collaborative Research Infrastructure
Strategy and Education Infrastructure FundSuper Science Initiative, through the Department
of Industr y, Innovation, Science, Research
and Tertiar y Education. Support was also
provided to TERN for these activities from the
Queensland Government. Work was carried
out under permit number WITK11870712
issued by the Department of Environment and
Heritage Protection, Queensland. We thank
the 47 volunteers, students and CSIRO staff who
helped with the census and data management,
especially D Glas, M Wenslaff and C Doyle. M
Karan (TERN) and J Addison (CSIRO) provided
useful comments on the initial manuscript.
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